The present invention relates to a joint for unfolding and locking space elements, and more particularly, two joint halves configured to be swivelled about a common axis and each connected with another one of two respective adjacent space elements, a detent lever configured as a locking element and swivellably disposed on one joint half and acted upon by an elastic force in a direction to the common axis, a guiding contour situated on the other joint half, spaced from the common axis and provided with a depression, and a guiding element resting on the guiding contour, in the folded as well as not completely unfolded condition of the joint, which guiding element is configured as a portion of the detent lever and which, in the unfolded condition, engages in the depression.
DE 32 15 434 C2 shows a joint where a locking mechanism is described for unfoldable satellite solar generators. The space elements to be unfolded and locked are represented there by the individual panels of the solar generator. A joint of that type comprises two joint halves which are each connected with one of two adjacent panels and which are arranged so that they can be swivelled about a common axis. On one joint half, a detent lever is swivellably disposed which is used as the locking element and is provided with a spring which acts between its end and the common axis and pulls the detent lever in the direction to the latter. On the other joint half, a guiding contour is situated which is guided about the common axis at a distance of a defined radius and is provided with a depression. A guiding element which is constructed as a portion of the detent lever, specifically a locking pin, rests in the folded condition of the joint against an outer portion of the guiding contour and slides on the latter during the unfolding operation. When the completely unfolded condition is reached, however, the guiding element finally engages in the depression constructed as a groove. Since the spring, which acts in the direction to the common axis, holds the locking pin in the groove, the locked condition is therefore achieved.
This known joint has play even in the unfolded and locked condition. Particularly in the case of a fairly large number of space elements, such as, solar generator panels, to be unfolded, this play will add up and therefore will have an unfavorable effect on the accuracy of attitude and the attitude control. This play is unacceptable on the long run.
It is, therefore, an object of the present invention to provide a joint which is completely without play after the unfolding and locking. This object has been achieved in accordance with the present invention by a joint having a cam with a first surface situated on the other joint half, a clamping nose configured as a portion of the detent lever and having a second surface, such that, after engaging of the guiding element in the depression and shortly before the reaching of the completely unfolded condition, the second surface slides onto the first surface and is there clamped, and a stop element which is movably disposed on one joint half so that, in the completely unfolded condition, the stop element is pressed onto a stop surface situated on the other joint half.
Although, DE 40 32 112 C2 shows a locking mechanism for unfoldable solar generators of satellites via which also a high freedom from play is to be achieved in the locked condition, this mechanism, at least in one important point, is based on a completely different fundamental construction from the present invention and also has important disadvantages. Thus, no swivellable detent lever is used there but a wedge which is acted upon by a spring tension, is equipped with a roller and rests against a guiding surface. During the unfolding operation, the roller is to roll off on the circular guiding contour which also exists there, until a plane section of the guiding contour is reached. The wedge is finally clamped in between the guiding surface and this plane section of the guiding contour. It is a disadvantage of this known construction that there is always the danger of a jamming of the roller and the wedge between the guiding surface and the circular guiding contour, specifically still during the actual unfolding operation. Although this can be avoided when all component parts are extremely carefully dimensioned, such a dimensioning is always threatened by unavoidable tolerances as well as unpredictable changes of the coefficients of friction which may occur under space conditions. This known concept therefore has certain operating risks which are avoided in the case of the present invention.
A significant advantage of the present invention consists of the fact that, at the end of the unfolding operation, the detent lever slides by its clamping nose onto the surface of the cam and clamps there in a tight manner, and simultaneously the stop element of one joint half is pressed against the stop surface of the other joint half so that, by way of the forces acting on these two contact surfaces, a bracing takes place of the two joint halves with respect to one another. Thus, the otherwise existing play is completely eliminated in the joint halves, in the joint bearing and in the lever bearing. As a result, the joint forms a rigid unit of high stiffness which is completely free from play.